1. Field of the Invention
The invention is in the field of fuel burning fluidized bed combustion systems. More particularly, the invention relates to an apparatus and method for the reduction of NOx emissions from a fluidized bed combustion system.
2. Description of the Prior Art
In the Carruba et al patent (U.S. Pat. No. 4,054,407), a fluidized catalyst bed is taught (col. 6, lines 29-30) for use in a method of two stage combustion employing a fuel containing nitrogen and a catalyst. The Carruba et al method comprises forming a first mixture of the fuel and an amount of air substantially less than the amount needed for complete combustion of all the combustible components in the fuel, and combusting this first mixture in a first combustion zone in the presence of a catalyst, having an operating temperature below a temperature that would result in any substantial formation of oxides of nitrogen or other fixed nitrogen compounds from atmospheric nitrogen present in the mixture, to form a first effluent. The first effluent is mixed with an additional amount of air at least sufficient for complete combustion of all combustible components remaining in the first effluent to form a second mixture, which is combusted in a second combustion zone below a temperature that would result in any substantial formation of oxides of nitrogen from atmospheric nitrogen. The present invention, by contrast, employs a non-catalytic but chemically reactive fluidized bed.
In the Tenner patent (U.S. Pat. No. 4,021,186), there is disclosed a method and apparatus for reducing NOx from non-fluidized bed furnaces. NOx produced by combustion of nitro-containing fuels is reduced by a forced draft burner operating with below stoichiometric mixtures of air and fuel in a primary combustion chamber, combustion being completed by controlled injection of secondary air near the outlet of the chamber.